What are Cirrostratus Clouds?

Cirrostratus clouds are high, thin clouds that form above 20,000 feet and are made
mostly of ice crystals. They sometimes look like giant feathers, horse tails, or curls of hair in the sky.
These clouds are pushed by the jet stream and can move at high speeds reaching 100 mph.

What do they indicate?
They indicate that a precipitation is likely within 24 hours.